Convection loop hot tub system

ABSTRACT

There is provided a portable spa pool or hot tub system which includes a tub suitable for human bathing, and a water heating unit capable of burning one or more fuels. The water heating unit is situated adjacent to the tub and connected to the tub through an upper and a lower piping means, the arrangement forming a convection circulation loop. The tub is optionally circular, and when empty capable of being lifted and carried by two persons. Optionally the tub is double skinned and of a rigid plastics material with insulation between the two layers of plastic.

TECHNICAL FIELD

This invention relates to hot tubs and spa pools.

BACKGROUND ART

Conventional spa pools or hot tubs work by continually heating and recirculating water from the heating unit to the tub or pool. In order to achieve adequate circulation, pumps are almost invariably used to convey water from the heating unit to the pool and back again—a forced loop circulation system. In almost all designs, the pumps run on electrical power. Further, because pumps continuously recirculate the same water for periods of weeks or months, build-up of algae and bacteria needs to be stopped or inhibited, usually by adding to the water chemical agents, e.g. chlorine.

Additionally, conventional spa pools take many hours to heat up to a usable temperature, and they are designed to be left filled and heated for weeks. Therefore such pools have ongoing costs in electricity and chemicals and ongoing time requirements from monitoring chemical levels and changing filters, whether they are being used or not. Also, the most commonly used disinfectant chemical, chlorine, can irritate a range of skin conditions, particularly eczema and psoriasis.

There are available freestanding conventional spa pools which fill from a hose, and plug into a domestic electrical socket. These are more portable than the built-in designs described above, but are still heavy to shift manually and not robust due to their complex electrical machinery. They are of course restricted to sites with electrical outlets.

Although the word “portable” is commonly applied to patented systems and/or selling descriptions of such units, the need for electrical connections and motors means that the use of the word ‘portable’ in those contexts has definite limits. For example, an electrically-dependant unit cannot be used in a remote outdoor location without an electric power supply being provided. Further, the weight and relatively fragile construction of such electrically-dependant systems realistically precludes them from being moved to such sites.

So called ‘portable’ spas or tubs have been developed around a number of differing but related principles. In U.S. Pat. No. 5,408,707 which describes a “portable” spa, the tub itself is collapsible and has a pump with jets. This spa is described as “portable” because the tub itself is “portable”. However, the unit utilizes a pump and therefore cannot be used without an [electrical] power source. U.S. Pat. Nos. 6,108,829, 5,815,854, 4,843,659, 6,357,059, 6,003,166, 6,058,521, 4,744,112, 5,791,106, and 6,412,123 all similarly describe a range of different spas and tubs all of which utilize pumps and other electrical fittings for pumped circulation and heating.

U.S. Pat. No. 4,621,613 describes a system for pool and spa heating and attempts to incorporate the advantages of convection loop flow into a complex heat exchange system whereby water is heated in a heat exchanger and is then introduced near the bottom of the pool or spa whereupon it rises to the surface.

All of the above patents employ the use of pumps and therefore electricity. In the strict sense they are not truly portable” units, as power is required at every location any prior art unit is moved to. In some of the above cases the spas are collapsible, and this then defines or limits the extent of their “portability.”

U.S. Pat. No. 4,455,997 (assignee Snorkel Stove Company) does describe a different design, with an underwater burner heating the water in a tub, which would not necessarily require an electrical connection. However, this style of hot tubs has an internal partition to separate off the underwater stove from the bathers, which means they must be bigger than the earlier described systems to fit the same number of bathers. Also the tubs are disclosed as being made of wood, so that for the same number of bathers they are heavy. In addition to these disadvantages their wood construction makes them less robust. They would not survive, for instance, being dropped on or rolled over rocky terrain. Furthermore the Snorkel Stove Company website quotes “about 4 hours, honest!” as the time necessary to assemble their kitset tub.

An additional disadvantage with wooden tubs, unless an internal liner is added, is that they rely on the expansion of water-absorbing wood against the restraining metal cooping bands to force the staves tightly together to achieve water-tightness, which can take days to fully occur.

Lastly, the water heating unit burns only wood, without the capability to use gas or other fuels. This has obvious disadvantages with respect to safety in, for instance, fire risk conditions or environments.

All references, including any patents or patent applications cited in this specification are hereby incorporated by reference. No admission is made that any reference constitutes prior art. The discussion of the references states what their authors assert, and the applicants reserve the right to challenge the accuracy and pertinency of the cited documents. It will be clearly understood that, although a number of prior art publications are referred to herein, this reference does not constitute an admission that any of these documents form part of the common general knowledge in the art, in New Zealand or in any other country.

It is acknowledged that the term ‘comprise’ may, under varying jurisdictions, be attributed with either an exclusive or an inclusive meaning. For the purpose of this specification, and unless otherwise noted, the term ‘comprise’ shall have an inclusive meaning—i.e. that it will be taken to mean an inclusion of not only the listed components it directly references, but also other non-specified components or elements. This rationale will also be used when the term ‘comprised’ or ‘comprising’ is used in relation to one or more steps in a method or process.

It is an object of the present invention to address the foregoing problems or at least to provide the public with a useful choice.

Further aspects and advantages of the present invention will become apparent from the ensuing description which is given by way of example only.

DISCLOSURE OF INVENTION

According to one aspect of the present invention there is provided a portable spa pool or hot tub system including:

-   -   a tub suitable for human bathing, and     -   a water heating unit capable of burning a fuel selected from the         group consisting of: solid fuel, diesel, other petroleum         product, and gas; said unit being situated and adjacent to said         tub and connected to said tub through an upper and a lower         piping means arranged such that water heated in the water         heating unit rises into the tub via the upper piping means and         is replaced by cooler water from the tub via the lower piping         means, the arrangement forming a convection circulation loop.

According to another aspect of the present invention there is provided a tub when used in a portable spa pool or hot tub system wherein the system further includes a water heating unit capable of burning capable of burning a fuel selected from the group consisting of: solid fuel, diesel, other petroleum product, and gas; said unit being situated and adjacent to said tub and connected to said tub through an upper and a lower piping means arranged such that water heated in the water heating unit rises into the tub via the upper piping means and is replaced by cooler water from the tub via the lower piping means, the arrangement forming a convection circulation loop.

The tub is of a size and form able to hold up to several human bathers. It may take the form of a rounded-edged double skinned insulated cylinder wider than it is high. The convection loop system employed also applies to more rectangular or convoluted shapes of tubs. The tub may be constructed of a range of materials but a preferred construction uses a foam spun plastic sandwich which is extremely robust and allows the vessel to be rolled or roughly handled.

The water heater/burner sits adjacent to the tub. It incorporates a water jacket and is connected to the tub by two hoses, the upper of which must rise at an incline from the burner to the tub. When firewood or other solid fuel or diesel or other suitable petroleum product or gas fire is lit in the burner, the water in the water jacket is heated and rises through the upper hose to the tub, being replaced by cooler water from the tub running back to the burner via the lower hose. This forms a convection loop which heats the tub water as the water continuously circulates through the lit burner. It does not require a pump, nor, therefore, electricity.

In the invention the traditional use of pumps is obviated by achieving a relatively high rate of ‘convection circulation’. This has been achieved by providing a reasonable circulation rate. The rate of heating is related in part to the vertical distance between the in and out ports to the hot tub, the insulation rating of the tub itself, and heater features which include but are not limited to corrugating the internal combustion chamber, which increases the surface area available for heat exchange, and an internal baffle to lengthen the flame trail for the same reason.

A very simple but efficient water heater design is used which is able to burn smoklessly and which does away with the complicated designs described in, for example, U.S. Pat. Nos. 4,501,232, 4,190,199 and 5,201,307, these designs being unsuitable for truly portable systems as they are too heavy to move. The same applies to any of the wooden tub designs. Invariably wooden construction results in designs that are not light enough to be moved by one person and which also lack the robustness necessary if they are to withstand routine or regular transportation to different sites.

In a preferred embodiment the system of the current invention the tub comprises a rigid structure of spun plastic foam core construction providing sufficient rigidity, lightness and strength for the unit to be rolled or moved by one person, or lifted and carried by two. The water heater is gas- or solid fuel-heated and is a separate module, which can be carried separately or stored for transport inside the tub.

As a result the tub/heater system is ideally suited for domestic houses, holiday cabins or cribs, weekend use, back country huts, beaches, boats, outdoor, and adventure use because no set-up ancillary requirements are needed at the (remote) site. The tub is adapted to be rolled along the ground by a single person, robust enough to sustain being bounced over rocky terrain or dropped from at least half a meter onto concrete without suffering structural damage. It can also be lifted and carried by two persons, or even floated and towed behind a boat. Assembling the system on site takes less than two minutes.

BRIEF DESCRIPTION OF DRAWINGS

Further aspects of the present invention will become apparent from the following description which is given by way of example only and with reference to the accompanying drawings in which:

FIG. 1: is an isometric view of the hot tub of the present invention showing the water heater and a gas fuel supply.

FIG. 2 is an isometric view of the hot tub of the present invention showing the heater, a gas fuel supply and burner nozzle.

FIG. 3 is an isometric view of the hot tub of a preferred embodiment of the present invention with the water heater part cut away showing the inside of the burner, air supply and flame baffle.

FIG. 4 is a cross sectional isometric of the hot tub of the present invention; and

FIG. 5 is an isometric view of the upper port of the present invention.

BEST MODES FOR CARRYING OUT THE INVENTION

FIG. 1 shows all of the basic components of a fully portable hot tub system of the present invention. The ‘hot tub’ comprises the tub (1), a water heater (2), and a fuel supply. In FIG. 1 the fuel supply is a 9 kg LPG gas bottle (3). However, it will be appreciated by those skilled in the art that the fuel supply can be selected from a range of solid fuels, with modifications to the water heater (2), for example as described below.

The water heater (2) is shown with an exhaust flue (4) which has an external perforated guard (5). Stabilizing legs (6) and (7), screwed onto the rear of the water heater (2) ensure that the water heater (2) remains upright when placed on the ground. The exhaust flue (4) may be free standing in the sense that no external support is required to stabilize the flue (4) other than the connection to the water heater (2).

A convection loop is created between the tub (1) and the water heater (2) by the interconnecting pipes (8) and (9). The pipes (8) and (9) may be removed to permit transportation of the system.

Large, easy to grasp handles (30, 31) are fixed on opposite sides of the water heater (2) to enable it to be easily transported by one or two persons.

A cowl (25) at the top of the exhaust flue (24) encloses a fly ash screen (not shown) upon which a place (26) (dotted outline) can be placed. The plate (26) may be used for cooking or heating purposes, for example, by the use of a pot (27).

FIG. 2 shows a secondary access door (10) to the water heater (2) in the open position. This allows a slotted gas burner head (11) to be inserted into the heating compartment of the water heater (2). The access door (10), which is mounted to a primary access door (12), is fixed by a pivot pin (13) and is rotatable with respect to the longitudinal axis of the water heater (2). The pivot pin (13) allows the access door (10) to be rotated to expose an opening in the primary access door (12). The primary access door (12) is able to opened, with the use of hinges (14, 15) and has a catch (16) for releasably securing the door (12) in a closed position. The use of the primary and secondary access doors (10, 12) permits the use of more than one fuel.

FIG. 3 shows the water heater (3) part cutaway, revealing inside a combustion chamber a gas burner head (11), a flame baffle plate (17) and an ancillary air supply (18). The ancillary air supply (18) provides fully oxygenated heated air to the rear portion of the heating compartment of the water heater (2). An outer water jacket (19) of the water heater (2) is also shown. The flame baffle plate (17) optionally extends to the sides, and along the bulk of the length, of the water burner (2). This arrangement assists with heat transfer to the water in the water jacket, and in reducing the flame length in the exhaust flue (4).

In a second embodiment, if a solid fuel (for example, wood, coal) is to be burnt in the water heater (2), a grate (not shown) can be inserted into the base of the water heater (2) in known manner.

Optionally, for both embodiments, the interior of the water heater (2), within the combustion chamber, is corrugated to assist in heat transfer to the water.

FIG. 4 shows a cut away view of the tub (1) revealing upper and lower access ports (20, 21) to the interconnecting pipes (8, 9) respectively. The upper port (20) is covered with a grill (22) which includes a floating disc (23). Referring to FIG. 5, the disc (23) moves up and down with the variation of the water level in the tub (1). The disc (23) moves over the port (20) when steam starts to enter the tub (1), deflecting the steam laterally to the interior of the tub wall. A stop (24) ensures the disc (23) settles in the correct position after the tub (1) has been moved.

The tub (1) is preferably cylindrical in shape, with a contiguous base. Optionally the cylindrical diameter is greater than the height of the tub (1). The tub (1) can be made of a plastics material, with the selection of the plastics being for appropriate rigidity and robustness of the tub (1) when used or moved. Optionally, the tub (1) is a double skin arrangement with an insulating layer of material between the two skins. The tub (1) may be of molded polyethylene, and the insulation a foamed core of a second plastics material. Optionally, the second plastics material is foamed polyurethane.

In an alternative embodiment, the necessary rigidity of the tub (1) can be imparted to the tub (1) by use of water-impermeable material and the tub (1) constructed in compartments which are capable of being inflated to provide the required rigidity. A suitable material for use in this embodiment is a polyvinylchloride plastic.

The material, shape and core (if present) of the tub (1) are sufficiently robust, and the tub (1) is sized so that the tub (1), when empty, can be lifted and carried by two persons or rolled on its side, by at least one person.

Whilst not shown in the drawings, it will be appreciated by those skilled in the art that the tub (1) may be supplied with a lid which fits over the tub (1) and be releasably secured to the tub (1), when the tub (1) is not in use.

Aspects of the present invention have been described by way of example only and it should be appreciated that modifications and additions may be made thereto without departing from the scope thereof. 

1. A portable spa pool or hot tub system comprising: a tub suitable for human bathing, and a water heating unit capable of burning a fuel selected from the group consisting of: solid fuel, diesel, other petroleum product, and gas; said unit being situated and adjacent to said tub and connected to said tub through an upper and a lower piping means arranged such that water heated in the water heating unit rises into the tub via the upper piping means and is replaced by cooler water from the tub via the lower piping means, the arrangement forming a convection circulation loop.
 2. A system as claimed in claim 1 wherein said tub has a circular side wall.
 3. A system as claimed in either claim 1 wherein said tub is constructed as a double skinned tub, with an insulating material between the skins.
 4. A system as claimed in claim 3 wherein the skins of the tub are of a plastic material.
 5. A system as claimed in claim 4 wherein the plastic material is polyethylene.
 6. A system as claimed in claim 3 wherein the insulating material is a foamed polyurethane.
 7. The system as claimed in claim 1 wherein the weight of the tub is such that two persons of average strength can lift and carry said tub, when empty.
 8. The system as claimed in claim 1 wherein the rigidity of the tub is imparted to the tub by use of a water-impermeable material and the tub constructed in compartments which are capable of being inflated.
 9. A portable spa pool or hot tub system as claimed in claim 1 wherein the water heater comprises a water jacket and a combustion chamber, the combustion chamber comprising a flame baffle plate and an ancillary air delivery means providing oxygenated heated air to the rear of the combustion chamber.
 10. A portable spa pool or hot tub system as claimed in claim 1 wherein the water heater further comprises a primary access door and a secondary access door, the secondary door being rotatable about the longitudinal axis of the water heater. 11 A portable spa pool or hot tub system as claimed in claim 9 wherein the ancillary air delivery means comprises a tube located through a hole in the primary access door.
 12. A portable spa pool or hot tub system as claimed in claim 1 wherein said water heater further comprises a flue, said flue having an outer guard and a fly ash screen within a cowl at the upper end of the flue.
 13. A portable spa pool or hot tub system as claimed in any one of claims 9 wherein the inner surface of the combustion chamber is corrugated.
 14. A tub when used in a portable spa pool or hot tub system wherein the system comprises a water heating unit capable of burning a fuel selected from the group consisting of: solid fuel, diesel, other petroleum product, and gas; said unit being situated and adjacent to said tub and connected to said tub through an upper and a lower piping means arranged such that water heated in the water heating unit rises into the tub via the upper piping means and is replaced by cooler water from the tub via the lower piping means, the arrangement forming a convection circulation loop. 